SARS-CoV-2 Novel Coronavirus Transmission electron micrograph of SARS-2 virus particles isolated from a patient. Image taken at the NIAID Integrated Research Facility, (IRF), Fort Detrick. Color-enhanced. Credit: National Institute of Allergy and Infectious Diseases (NIH).
Researchers from the University of Liverpool demonstrated how SARS-CoV-2 virus proteases attack host cells and how they can be targeted to prevent replication of the virus in cultured cells using existing drugs.
Nature Communications published the new findings today. They provide a valuable resource for understanding proteolysis in the context virus infection and inform the development of targeted strategies that inhibit COVID-19.
SARS-CoV-2 was responsible for more than 227 million infections and more deaths in the world during the pandemic. Improved understanding of SARS-CoV-2's basic biology is a boon for vaccine development and testing.
SARS-CoV-2 replication is influenced by both viral and cellular proteases. Inhibitors targeting proteases have been shown to be effective in reducing SARS-CoV-2 cell culture models.
Researchers used mass spectrometry to examine proteolytic cleavage processes during SARS-CoV-2 infected.
"Mass spectrometry-based methods to identify protease substrats have been around for a while, however, they have only seen limited application to study of viral substrates and had not previously been applied to study proteolysis during coronavirus infected," explains Dr. Emmott Ed, a Tenure Track Fellow at the University's Institute of Systems, Molecular and Integrated Biology.
The team discovered previously unknown cleavage points in several viral proteins, including the major antigenic proteins S & N. These are the main targets of vaccine and antibody testing efforts.
They found significant increases in cell cleavage events consistent to cleavage of SARS-CoV-2 main protease (Mpro). Additionally, they identified 14 potential high confidence substrates for the main and papain-like proteases. One subset was validated with in vitro assays.
They also showed that siRNA depletion caused SARS-CoV-2 to stop replication and that drugs targeting two proteins, the Ser/Thr kinase kinase SRC, and MYLK, resulted in a dose-dependent decrease in SARS CoV-2 titres.
Bafetinib, an experimental cancer drug, and Sorafenib, an approved drug to treat kidney and liver tumors, showed SARS-CoV-2 inhibitory levels that didn't cause cytotoxicity in a human cell model of infection.
Dr. Emmott stated that it was crucial to understand the precise mechanisms by which proteolytic cleavage regulates protein activity and benefits viral replication in order to target cellular substrates for viral proteases as therapeutic strategies.
"As more SARS-CoV-2 variants become available, the incorporation data from post translational modifications studies such as these can support efforts to predict phenotypes using genetic data on emerging variants."
Continue reading: Virologists release new information on SARS-CoV-2 treatment options
More information: Nature Communications (2021) Characterizing proteolysis during SARS/CoV-2 infection identifies virus cleavage site and cellular targets with therapeutic potency, Information from Nature Communications: Characterising proteolysis in SARS-CoV-2 Infection identifies viral targets and cleavage sites with therapeutic potential, (2021). DOI: 10.1038/s41467-021-25796-w
